A number of different type single effect solar evaporation stills have been used primarily to distill sea water. One such type of sea water still utilizes an inclined or tilted floor member on which the sea water is fed to a porous covering and evaporated therefrom by impinging solar radiation. The purified water vapor condenses in the solar distillation apparatus on the inner surface of a transparent roof member. Wall members extending between said floor and roof members in solar stills of this general type all provide only a few inches of spacing so that the distilled water vapor proceeds primarily through turbulent mass flow to the roof condensing surface which serves exclusively as the distillate condensing and collecting surface.
Operating efficiency of the known single-effect horizontal or bay-type sea water stills has also been reported. A 1967 report describes the operation of a horizontal or basin-type still on the Aegean Island of Patmos and having 8,667 square meters of evaporating surface area produced 6,884 gallons per day of distilled water or three liters per square meter of evaporating surface area. A 1976 report describing operation of a different basin-type still construction in Giza with 27 square meters of evaporating surface area per unit also produced distillate at approximately 3 liters per square meter per day operation for an isolation rate of 5,950 kilocalories per square meter per day. The production efficiency of these horizontal stills can be computed using the heat of evaporation of water as 565 calories per gram to yield an efficiency of less than 30%. A more efficient inclined plane sea water still has also been reported as yielding 4.48 liters per square meter of evaporating surface area per day at an insolation rate of 5,430 kilocalories per square meter per day, to yield an efficiency of approximately 45%. The insolation was measured at the plane of the still which was inclined 30.degree. to the horizontal elevation. The construction design for said improved inclined floor still included a distilland absorbing covering on the floor member in the form of glass fibers pressed into black colored plastic and a 21/2 inch spacing existed between the floor and roof members of the apparatus. Problems encountered in the operation of this still design included non-uniform wetting of the distilland absorbing surface and surface fading due to the solar exposure which both reduced the operating efficiency of the apparatus considerably below a 45% efficiency within a few weeks.